Do something about international during performance, saying nothing (8)
I believe the answer is:
taciturn
'saying nothing' is the definition.
(taciturn means saying very little)
'do something about international during performance' is the wordplay.
'do something' becomes 'act' (to act is to do something).
'about' indicates putting letters inside.
'international' becomes 'i' (abbreviation eg in IMF).
'during' is an insertion indicator.
'performance' becomes 'turn' (turn is a kind of performance).
'act' enclosing 'i' is 'acit'.
'acit' going into 'turn' is 'TACITURN'.
(Other definitions for taciturn that I've seen before include "Without saying much" , "Aloof" , "Uncommunicative, of few words" , "Habitually silent" , "withdrawn" .)